Recent advances have shown that nanometer-sized semiconductor particles can be covalently linked with biorecognition molecules such as peptides, antibodies, nucleic acids, or small-molecule ligands for applications as fluorescent probes. In comparison with organic fluorophores, these quantum-confined particles or quantum dots (QDs) exhibit unique optical and electronic properties, such as size- and composition-tunable fluorescence emission from visible to infrared wavelengths, large absorption coefficients across a wide spectral range, and very high levels of brightness and photostability. Due to their broad excitation profiles and narrow/symmetric emission spectra, high-quality QDs are also well suited for optical multiplexing, in which multiple colors and intensities are combined to encode genes, proteins, and small-molecule libraries.
Therefore, the development of high-sensitivity and high-specificity probes beyond the intrinsic limitations of organic dyes and fluorescent proteins is of considerable interest to many areas of research, ranging from molecular and cellular biology to molecular imaging and medical diagnostics.